Method of preparing metallic sulphates from sulphide ores and the like



March 16, 1937. J. H. CALBECK METHOD OF PREPAR ING METALLIC SULPHATESFROM SULPHIDE ORES` AND THE LIKE Filed April l5, 1955 Patented Mar. 16,1937 METHOD 0F PREPARING METALLIC STIL- PHATES FROM SULPHIDE ORES ANDTHE LIKE John Henry Calbeck, Columbus, Ohio, assignor to American Zinc,Lead & Smelting Company', St. Louis, Mo., a corporation of MaineApplication April 15, 1935, Serial No. 16,521

14 Claims.

This invention relates to the preparation of metallic sulphates frommetallic sulphides and has as its principal object the conversion ofsuch sulphide ores as sphalerite, galeria, pyrite, etc., intocorresponding sulphatesk. This invention is based on my discovery thatif a metallic sulphide` ore, such as ZnS, is heated with ammoniumbisulphate, the sulphide is converted into the sulphate of the metal andthe ammonium salt is 'l0 reduced to the sulphite, sulphur andv wateraccording to the following equation: l

ZnS+2NH4HSO4=ZnSO4+ (NH4) zSOs-l-Sq-Hzo I have discovered that .thisreaction begins at temperatures between 150 C. and 200 C., but thereaction is most rapid and the most satisfactory results are obtained atbetween 350 C. and 440 C.,\ at which temperature the ammonium sulphiteand sulphur are easily volatilized andmay be condensed and collected byappropriate means.

It is not necessary to use temperatures as high as 440 C., which is theboiling point of sulphur, for l the reason that the sulphur is somewhatvolatile in the ammonium sulphite and at 350 C.,'al1

V the sulphur will pass over with the ammonium sulphate. I am aware ofthe fact that ammonium sulphite isprobably dissociated in the vaporphase and is in reality only a mixture of NH3 gas and SO2 gas and watervapor, but

throughout the description I shall refer to the ammonium sulphite as ifit were completely volatile as such in order to obtain clarity andbrevity.

The invention has for its further object the control of the abovedescribed reaction so las 'not only to obtain complete sulphation of themetallic sulphide but also to obtain economy in the use of ammoniumsulphate, and further, to obtain the volatile products driven offduring' the reaction in a condition in which they 'may be readilymarketed or used. vThe method of the inventionv is particular/1y adaptedto the production of thel water soluble sulphates, such as copper andzinc,

, which are used extensively in hydrometallurgical andelectrometallurgical processes as well as having an extensive market inthe forium.Ssulphates.-Y

` sulphate which may be-used as an anticolor in industry or which may beused inthe manufacture of zinc sulphide pigment, according to the (Cl.Z3-125) method outlined in my copending application, Serial No. 688,413.

In order to describe the'invention in detail, the treatment of zincsulphide ore will be given as an illustration, but it will be understoodthat the invention is equally efficient for the treatment of othermetallic sulphides for the purpose of preparing the correspondingsulphates. Zinc sulphide concentrates are nely ground and mixed withnely ground ammonium bisulphate. The required amount of ammoniumbisulphate is determined from the analysis of the zinc concentrates andshould equal or slightly exceed two chemical equivalents of ammoniumbisulphate for each chemical equivalent of zinc lead, iron and limecontained in the ore. This mixture is now charged into 'a mechanicalmuflle furnace, prefsalt cake from sodium'bisulphate and common salt.The charge may be passed through the iurnace continuously or it may betreated as a batch. In the former case, the temperature should bemaintained at `between 350 C. and 440 C., and in the latter case, thetemperature should be gradually increased until a maximum tempera'- tureoi 440 C. is obtained and held there until the reaction is complete.

At the beginning of the reaction, the ammonium bisulphate fuses,'forminga pasty mass, and rapid heating should be avoidedat this stage toprevent rapid evolution of the volatile products from causing excessivefrothing or boiling over.

Toward the end of the reaction, the charge becomes slid and, under' theaction of the rabbles of the furnace, is broken up so that at the end ofy n 4 the reaction it may be discharged from the fur- "nace as smallwhite grains, consisting largely. of

` formed may be purified of the various impurities by methods well knownin ythe electrolytic zinc orlithopone industries., t During the heatingin the mulile furnace there Vis v'a steady evolution offthe volatileproducts,

which may be Acollected in various 'well known ways, depending upon thenature of the product s desired and the use to which it is to bel put.It

is common to collect such fume`r` or-volatile products in water and bypassing these products` 10 of ammonium thiosulphate. As far as I amaware, a sublimed or fumed ammonium thiosuiphate has never before beenprepared. It is well known that ammoniumsulphite and sulphur react' inaqueous solution to form ammo- 15 nium thiosulphate, but to preparethesalt from solution, evaporation under a vacuum must be resorted toand great care taken to prevent the decomposition of the salt. But Iprefer to collect the volatile products in the form of a sub- -20 limatewhich consists of pure white, crystals of ammonium thiosulphate, andwhich need no further treatment in order to condition them for market.

'I'he sublimate is best collected in a jacketed 25 steel tower. Beforethe sublimation is begun,

hot air is passed through the jacket of the towerA to bring thetemperature within the tower up slightly above 100 C. in order toprevent moisture condensing with the sublimate. As the sublimate beginsto condense in the tower, the temperature rises and cold airis passedthrough the jacket as required to keep the temperature within thedesired limits, 100 C.-150 C. I have discovered that the ammoniumthiosulphate is not completely formed just as the sublimate condenses,but that some time is lrequired for the reaction between the sublimedsulphur and the sublimed ammonium sulphite to be completed. 40 In orderthat this conversion may .be complete `and that the iinal productcontain a high percentage of thiosulphate and avery small per: centageof uncombined sulphite, it is highly important that the fumepassing'intothe sublimate condenser shallhave yexactly .chemicallyequivalent proportions of ammonium sulphite and elemental sulphur at alltimes. In ordery that this may be accomplished, a numberof veryimportant precautions should be taken:

1. The system should bekept free of" air .or other oxidizing gases.

A slight positive pressure on the system cony sisting of the muilleand\sublimate condenser will be of considerable help in this regard. Forthis 55 'purpose I prefer to addga little ammonium sulphate to thecharge. This ammonium sulphate breaks downin the ammonia gas andammonium bisulphate according to the following equation:

The ammonia gas so generated prevents the in filtration of air andyanyexcessof ammonia may be collected in water in tower or in an absorberconnected with the sublimate condenser.

2. The rate of volatilization and the temperature must be adjusted sothat the sulphur gen# erated by Reaction (1) will passover with theammonium sulphite as rapidly as itis formed.

,' Of course, if the temperature is kept at 440 C.

70 or above,' the sulphur will pass into the vapor phase as rapidly asformed and be carried over into the sublimation tower with the othergases.

But if the charge is well agitated the sulphur' will be taken over withthe evolved gases at lower temperatures than its boiling point and thisis desirable in order to prevent the sublimation of some ammoniumsulphate which is somewhat volatile at the temperature of boilingsulphur.

3. The sublimate in the tower should be mainto add a certain amount offree sulphur and to substitute ammonium sulphate to produce NH3(Equation (2)) for part or all of the ammonium bisulphate called for inEquation (1). The sulphur reacts with the oxygen to form SO2 and thisSO2. reacts with free ammonia and excess elemental sulphur to formammonium thiosulphate.

Ii' these precautions are taken the sublimate collecting on the wallsand in the hopper of the tower will consist of between 90% and 99%ammonium thiosulphate inthe form of a dry snow white cake which iseasily removed and packed in containers. A

The preparation of the ammonium bisulphate employed may be by the wellknown method of boiling ammonium sulphate in a pot or kettle until thefree ammonia is boiled oi, according to Reaction (2). The molten mass ofNH4I-ISO4 may be cooled in pans or flaked and the solid bisulphatepulverized and is ready for charging with the sulphide ore. However, Ihave found it more convenient to charge the ammonium sulphate into themechanical furnace with the sulphide ore and allow both Reactions (1)and (2) to take place together. Combining the two equations, we obtainthe following, which represents the reaction between a metallic sulphideand ammonium sulphate.

This reaction goes forward rapidly at a temperature of between 350 C.and'400 C. The

zinc sulphate remains in the furnace, the ami K consisting of a muiilesection 2 surrounded by ues 3 through which hot gases from theiire box 4circulate. The muille section 2 is provided with a feed hopper 5. bymeans of which. the material to be treated is supplied to the muiilesection 2, and a discharge pipe 6 and a suitable raking device 1. Asublimate condenser 8v is connected to the muflie section 2 by a pipe 9,and said tower is provided with a jacket I0 through which hot or coldair, as may be required, is circulated by, means of a fan Il to regulatethe temperature within the tower. An ammonia absorption tower l2 isconnected to the sublimate condenser 8by a pipe Il. The tower l2 is'partially iiiled 4 n 2,074,210 Y with water through the valved inletI2. This make the dense ammonium thiosulphate liquor tower I2 is open tothe air through a pipe I4 and fan I5 which discharges to the open air.Provision is made to circulate the water through the tower I2 by meansof a pump I6 which takes -water from the bottom of the tower throughpipe I1 and passes it through the cooling coil I8 and pipe I9 anddelivers it into `the top of the" tower at 20. The coil I8 is locatedina tank2I 10 through which cold water or other cooling media may Irecirculated, entering through pipe 2| and passing out through pipe 2l".Flow of gas through the system is regulated by a damper 22 Il. in thepipe An example of a typical continuous operation is as follows:

A charge is prepared by mixing 350 poundsflne flotation zincconcentrates, 800 pounds commercial ammonium sulphate and pounds pul- 20verized sulphur. The furnace is maintained at .a

by turning on the pump begin to pass of! at once into the towers 8 andI2.

45 th'e bottom of the tower.

The sulphur and ammonium sulphitel condense together in the sublimatecondenser 8, and the /ammonia gas passes on into the absorption tower I2where it is dissolved in the cold water. In a short time, thetemperature in the sublimate condenser begins to risc and a current ofcold air is circulated in the jacket I Il of the sublimate condenser atthe proper rate to keep the temperature below 150 C. but above 100 C.Theammonia gas dissolves in the water of the absorption tower I2 withthe evolution of heat, and this heat is dissipated by passing the waterfrom the tower I2 through the :,:oolirlg coils I8. As the deposit ofsublimate grows in the tower 8, 'it falls from the walls and collects ina suitable hopper 8' at Occasional rapping on 8 may be necessary to thewalls' of thetower l the walls from becoming prevent the deposit' on"-so-.thick as to prevent the dissipation of the heat through the walls.The sublimate may be re- 50 moved from the hopper at the lower part ofthe tower from time to time as required, care being taken to admit aslittle air as possible in the operation.` As the concentration ofammonia in solution in the absorption tower I2 builds up to a comercialconcentration, the solution is removed through any suitable dischargeopening, as for example, a spigot 28, and the solution thus removed'frcmthe tower is replaced with water. The movement of the rakes in themuiile section 2 center outward to the periphery whence thenonvolatilizedi part is discharged through the pipe 6. The rate of feedof the charge to the furnace should beso adjusted that this dischargeconsists only of zinc sulphate and the gangue constituents of the ore,such as silica, calcium, sulphate. etc. The zinc sulphate thus`discharged is anhydrous and porous and -dissolves readily in water withthe evolution of heat, and this water solution may be purified by wellknown methods, such as are commonly used in purifying zinc sulphateliquors. The dry ammonium thiosulphate sublimate discharged from thesublimate condenser 8 maybe marketed in the form in which it leaves7seidtowenoritmeybedissolvedinwaterto of the furnace slowly works thecharge from the required for the manufacture of zinc sulphide. Theammonia water solution withdrawn from the tower I2 may be used as a basein the zinc s ulphide process of my application Serial No. 688,413,

- or it may be marketed as aqua-ammonia.

In case it is desired to separate the sulphur fume from the ammoniumsulphite fume, this can be done by using two sublimate condensers,similar to the tower 8, the two towers being connected in tandem. Inthis case the rst tower should be maintained at a temperature between200 C. and 350 C. and the second chamber below 200 C. In this case asublimate collects in the first chamber consisting almost entirely ofelemental sulphur and in the second tower a sublimate collectsconsisting `almost entirely of ammonium sulphite.

It is not essential to collect the ammonium thiosulphate as a drysublimate but it 'may be collected in water to form an aqueous solution.To

do this it is only necessary to replace the sub- Q limate condenser withanL absorption tower similar to the tower I2. In this case thetemperature of the solutionshould be maintained near` 100 C. so that thefree ammonia may be driven over into the ammonia absorption apparatus.

It will be apparent to those skilled in the art that certainmodifications and variations of the process, as illustrated in theforegoing example, may be practiced without departing from the spirit ofthe invention as defined in the appended claims, and such modificationsand departures as fall within the terms o f said claims are intended tobe covered thereby.

What is claimed is:

1. In a method of preparing-a metallic sulphate from the correspondingmetallic sulphide, the step which consists in calcining the sulphidewith an ammonium sulphate at a temperature sufficiently high tovolatilize allwreaction products except the sulphates.

2. In a method of preparing a metallicsulphate V from thecorresponding'metallic' sulphide, the step which consists in calciningthe sulphide with an ammonium sulphate at a 'temperature sufficientlyhigh to volatilize the ammonium reaction products but not high enough toappreciably volatilize the ammonium bi-sulphate -or decompose metallicsulphate.

- 3. In a method of preparing -anhydrous zinc sulphate from zincsulphide ore,` the step which consists in calcining the zinc sulphideore with ammonium sulphate atV a temperature suficiently high tovolatilize the ammonium reaction products but .not highenough toappreciably decompose zinc sulphate.

n 4. In a method of preparing anhydrous zinc sulphate and ammoniumsulphite the step which consists in calcining zinc sulphideore with twochemical equivalents of ammonium bisulphate in the absence of oxygen andat a temperature high enough to volatilize ammonium sulphite but nothigh enough to volatilize ammonium bl-sulphate.

quantities, which comprises calcining zinc sulphide with twice thechemical equivalent quantity of ammonium sulphate in the absence ofoxygen and at a temperature between 150 C. and 440 C., and passing thevolatile products ilrst through a tower heated slightly above 100 C. tocollect the ammonium sulphite and sulphur and then passing the remainingvolatile products from the tower through cold water to collect theammonia. v

'It A method of preparing ammonium sulphite which comprises calcining ametallic sulphide 'with an ammonium sulphate at a temperature highenough to volatilize ammonium sulphite, but not high enough tovolatilize ammonium bi-sulphate nor decompose the metallic sulphate iformed,fand' collecting the ammonium sulphite.

8. A method of preparing ammonium sulphiteV and sulphurin chemicallyequivalent proportions l for the purpose of preparing ammoniumthiosultemperature high enough to volatilize ammonium sulphite andsulphur but not high enough to volatilize ammonium bisulphate, andcondensing the resulting ammonium sulphite and sulphur fumes together ina dry chamber at a temperature slightly above 100 C.

9. A method of preparing anhydrous ammonium thiosulphate which comprisescalcining zinc sulphide with twice the chemical equivalent quantity ofammonium sulphate at a temperature between 150 C. and 440 C. in theabsence of oxygen, condensing from the resulting Volatile products almixture of ammonium sulphite and sulphur in chemically equivalentquantities at a temperature above 100 C. and holding the resultingsublimate at that temperature until substantially all the ammoniumsulphite has been converted into ammonium thiosulphate.

monia in substantially chemically equivalent l0. A method 'of preparingammonium thiosulphate which comprises calcining zincv sulphide withtwice the chemically equivalent quantities of ammonium bisulphate at atemperature lbetween l C. and 440 C. in the absence of oxygen,sublimating the ammonium compounds and leaving a calcine of anhydrouszinc sulphate, then collecting the sublimates of-sulphur and ammoniumsulphite and converting them to ammonium thiosulphate.

.11. A non-aqueous method -of preparing ammoniumthiosulphate, whichincludes subliming ammonium sulphite and sulphur inchemically equivalentproportions and condensing at a temperature above C. and maintaining thesublimates at that temperature until substantially all the sulphite hasreacted with the sulphur to form 13. The method of recovering elementalsul- JOHN HENRY CAIBECK.

